SEOUL (AFP) - An envelope containing white powder was mailed to the US embassy in Seoul this week and is being tested for possible toxins, South Korean police said Thursday. Eighteen other US embassies have received white powder this month, as well as more than 40 governors' offices in the United States. Initial tests showed the substance was harmless but the deliveries sparked security alerts. South Korea's National Police Agency said an envelope postmarked Texas was delivered to the embassy Wednesday morning and has been taken away for testing. The Korea Centres for Disease Control and Prevention said most tests showed no harmful substance but details would be revealed after further examination. The embassy in Seoul is the second US mission in Asia to have received the sustance, after Tokyo. The Federal Bureau of Investigation, which is investigating the mailings, has said the letters were all similar and postmarked from Texas. In 2001 letters containing anthrax killed five people in the United States and spread panic. Since then, police and fire officers have been called out to investigate suspicious mailings across the US " most of them harmless.